Benoit,
I have to say it's a frightening story to see. Essentially a third party company (the SIP provider) locked themselves into another third party provider (Maxmind/geoiplookup) and now it's your job to fix the latter's mistake?
Besides being a tricky situation to cleanup for two third parties, it shows how critically centralised the Internet has become.
If a single private party can render your services unusable, the distribution of weights in the Internet is completely out of balance.
Best regards,
Nico
-- Sustainable and modern Infrastructures by ungleich.ch